The present invention concerns a tensioning device for traction means, particularly chains. Such chain tensioners are used, for example, for tensioning the timing chain and for tensioning the chain of auxiliary units of diesel and Otto engines.
A chain tensioner of the pre-cited type is known, for example, from DE-A 195 36 643. A tension shoe is mounted on a pivot axle for pivoting relative to a base element. A spring means is arranged between the tension shoe and the base element to urge the tension shoe against the chain. The tension shoe comprises a closed mounting eye into which the pivot axle fixed to the base element is axially inserted. A perfect centering of the mounting eye with the pivot axle is required for the assembly of the base element and the tension shoe. Centering is achieved by a relative displacement of the base element and the tension shoe. After the centering operation, the pivot axle can be inserted into the mounting eye by an axial displacement of the base element and the tension shoe relative to each other. Thus, for assembling these elements, it is necessary to operate in different planes, and this is particularly disadvantageous in automated mounting.
It is therefore the object of the present invention to simplify the assembly of the two elements. The invention achieves this object by the fact that one of the elements comprises at least one mounting eye having a radial mounting aperture for radially receiving the pivot axle arranged on the respective other element. In the tensioning device according to the invention, the assembly of the two elements is effected in one plane or in parallel planes. The base element and the tension shoe must be aligned to each other only in such a way that as a result of relative radial displacement between the elements, the pivot axle engages into the radial mounting aperture and thus into the mounting eye. If the radial mounting aperture has a flared mouth, the introduction of the pivot axle is further simplified. In particular, radial displacements in a plane perpendicular to the one plane are not required. It is understood that the invention also applies to tensioning devices in which a tension roller is used in place of a tension shoe and is mounted for rotation on a lever which comprises the mounting eye according to the invention for receiving the pivot axle.
In other words, the tensioning device of the invention for a traction means is comprised of a tensioning shoe (1), that tensions the traction means, and comprising a further base element (3), on which the tensioning element (1) is mounted for pivoting on a pivot axle (2), a spring means (4) arranged between the elements (1, 3) urging the tensioning element (1) against the traction means, wherein one of the two elements (1, 3) comprises two horseshoe-shaped spaced-apart fork arms (5, 10) each of which comprises a mounting eye (6, 11) having a radial mounting aperture (7, 12) for radially receiving the pivot axle (2), and the other of the elements (1, 3) comprises a radial projection (1, 3) which engages between the forks (5, 10) and is overlapped by the forks (5, 10) on both the elements (1, 3) for snap engagement without a separate fastener, there are corresponding arranged retention surfaces (8, 9) which extend coaxially with the pivot axle (2) and which, within an operation-dependent pivoting range of the tensioning device, are situated opposite each other and face each other, a radial displacement of the pivot axle (2) out of the radial mounting aperture (7, 12) being prevented by a contact of the retention surfaces (8, 9) with each other.
Further embodiments of the invention offer other special advantages over prior art solutions. If one of the two elements comprises two spaced-apart fork arms and each of these fork arms comprises a mounting eye having the radial mounting aperture, the respective other element comprises a radial projection which is arranged between these fork arms and overlapped by both fork arms. Thus, after the assembly of the two elements, an axial slipping-apart of these elements is reliably prevented. In the prior art chain tensioner, it is necessary in some cases to use additional securing elements, for example a locking ring, which can be mounted only after the assembly of the two elements.
The pivot axle may be fixed, for example, on the base element and have ends projecting from both sides of the base element. Each of these ends then engages into one of the radial mounting apertures of one of the fork arms which are fixed on the tension shoe. The pivot axle may be made, for example, in one piece with the base element out of plastic. An equivalent solution consists in that the pivot axle is fixed on the tension shoe and has ends projecting from both sides of the tension shoe. Each of these ends then engages into one of the radial mounting apertures of one of the fork arms which are fixed on the base element. The tension shoe and the pivot axle can be made without any problem in one piece, for example, out of plastic.
Making the pivot axle in one piece with one of the two elements offers further advantages over prior art solutions. In prior art solutions, a separate pivot axle made of a metal is pressed into the base element. This necessitates the machining of a reception bore in the base element. Besides this, means have to be provided for securing the pin from falling out of the reception bore. This can happen if the pin and the base element are made of different materials having different thermal expansion properties and the tensioning device is subjected to high temperatures. All of these measures can be avoided if the pivot axle and the element concerned, i.e. the base element or the tension element, are made in one piece with each other. It goes without saying that these advantages are also obtained if, as in the prior art, the mounting eye for receiving the pivot axle has a closed configuration in peripheral direction.
To prevent the pivot axle from being displaced radially out of the mounting eye, it is proposed to arrange on both the elements, retention surfaces which extend coaxially with the pivot axle and which, within an operation-dependent pivoting range of the tensioning device, are situated opposite each other and face each other. A radial displacement of the pivot axle out of the radial mounting aperture is prevented by a contact of the retention surfaces with each other. The retention surfaces can be made by providing a convex retention surface on the tension shoe and a concave retention surface on the base element. Outside of the operation-dependent pivoting range of the tensioning device, the tension shoe can take a position of pivot relative to the base element in which the convex retention surface is disengaged from the concave retention surface. In this position of pivot, the pivot axle can be removed without any problem in radial direction out of the mounting eye. It is also possible to assemble the tension shoe and the base element in the said position of pivot. When the pivot axle has come into its pre-defined position in the mounting eye, the tension shoe can be pivoted about its pivot axle till the retention surfaces come to be situated opposite each other. In this arrangement, the pivot axle is retained perfectly in the mounting eye.
In the position of pivot intended for the assembly of the base element and the tension shoe, an additional securing device may become necessary for preventing the pivot axle from slipping radially out of the mounting eye. This is the case, for example, when the chain tensioner, pre-assembled in the above manner, has to be transported. It is adequate, in this case, to provide a constriction on the radial mounting aperture with a clear width smaller than the diameter of the pivot axle. In this embodiment of the invention, the pivot axle snaps into the mounting eye and a radial slipping out of the mounting eye is only possible by application of a higher force.
The embodiments of the invention described herein create tensioning devices for traction means which do not require additional securing means after the assembly of the base element and the tension shoe; the pivot axle is reliably retained in the mounting eye in a simple manner.